1. Field of the Invention
This invention relates to a high frequency signal receiver to be typically installed in a tuner of a television receiving set.
This application claims the priority of the Japanese Patent Application Nos. 2003-173822 filed on Jun. 18, 2003 and 2004-146917 filed on May 17, 2004, the entirety of which is incorporated by reference herein.
2. Related Background Art
As a radio wave for digital broadcasting using a broadcasting satellite (to be referred to as BS hereinafter) or a communications satellite (to be referred to as CS hereinafter) is received by a parabolic antenna, it is converted into a high frequency signal (RF signal) of 1 to 2 GHz and then the signal is sent to the high frequency signal receiver of a so-called set top box or tuner having a functional feature of receiving satellite broadcasting. The high frequency signal receiver is provided with a frequency converter for down-converting the RF signal input from the antenna into a signal with a predetermined frequency by mixing it with a locally oscillated signal coming from a local oscillation circuit.
With the trend of producing high density integrated circuits (to be referred to as IC hereinafter) in recent years, ICs that are used as frequency converters are often made to integrally comprise a frequency conversion circuit and a PLL circuit. Particularly, so-called direct conversion type ICs have been developed for frequency converters to be used for tuners for BS and CS broadcasting because they are adapted to directly down-covert the RF signal input to it by way of an antenna into a base band signal without requiring converting it into an intermediate frequency signal (IF signal).
For example, Patent Document 1 (Japanese Patent Application Laid-Open Publication No. 2002-190750) describes a direct conversion type frequency converter adapted to be installed in a tuner in a television receiving set.
Meanwhile, when a frequency converter is prepared by using a direct conversion type IC, the frequency of the signal output from a local oscillation output circuit is between 1 and 2 GHz, which is same as the frequency of the RF signal of the desired and selected channel coming from the antenna. An oscillator that directly oscillates such a high frequency wave of 1 to 2 GHz requires the use of costly parts and additionally can be influenced by distributed capacities and inductors so that it is difficult to regulate it and make it operate stably. For this reason, it has been conceived to use an source oscillator that oscillates approximately at a frequency in the so-called VHF or UHF frequency band and taking out a higher harmonic, e.g., fourth harmonic, of the oscillation output of the source oscillator and using it as locally oscillated output signal.
When a higher harmonic, e.g., fourth harmonic, is used for a locally oscillated output signal and if higher harmonics other than the fourth harmonic required for direct conversion are also input to a mixer circuit and the RF signal from the antenna contains a broadcast signal of the channel that corresponds to any of the unnecessary higher harmonics, the broadcast signal is also converted into a base band signal by frequency conversion.